One problem that is encountered during the use of low viscosity, high equivalent weight polyols to make PUR and PUR/PIR foams is a slow rate of cure, which generally results in surface friability and reduced processing speeds when the foam is used in the manufacture of laminate foam board. Surface friability in turn contributes to reduced adhesion to the facing sheet normally applied to the foam surface during manufacture of the foam board.
Another problem encountered, especially with polyols derived from DMT process residue, is compatibility of the polyol with the trichlorofluoromethane blowing agent commonly used in foam formulations. Low viscosity aromatic polyester polyols with improved blowing agent compatibility are described in U.S. Pat. No. 4,758,602 (Trowell). These polyols are prepared by reacting tall oil fatty acids with an aromatic polyester polyol, e.g., the reaction product of dimethyl terephthalate process residue and diethylene glycol, in the presence of a catalyst. However, the acid number of these polyols is higher than desired for the manufacture of rigid foams, and foaming is too slow.
U.S. patent application Ser. No. 200,982 to Panchak filed June 1, 1988 discloses a mixture of polyester polyol and 5-15 weight percent propylene or ethylene carbonate to reduce the viscosity. No chemical reaction occurs. After the addition of the propylene or ethylene carbonate to the polyester polyol, the modified polyol is ready for use in the production of laminate foam boards.
Polyols that have a low acid number and are readily soluble in chlorofluorocarbon blowing agents and that rapidly produce rigid foams that have good dimensional stability, good flammability characteristics and good compressive properties without the disadvantages of slow cure rate and surface friability would be desirable.